Fuel cell systems convert hydrogen into electrical power while emitting only water and heat. Fuel cells based on proton exchange membranes (PEM) generally need to be humidified to conduct protons. Concurrent conduction of protons through the electrolyte and conduction of electrons through an external load is the working principle of fuel cells.
Because membranes in PEM fuel cells need to be humidified and because fuel cells produce water, water is always present in fuel cells. This causes problems for fuel cells operating or stored at temperatures below the freezing point of water (0° C.). A first problem is the possible freezing of water in cells, humidifiers and gas tubing, blocking the passage of gases upon start-up. A second problem is the possible damage to membranes, membrane electrode assemblies (MEA) and fuel cell humidifiers due to the formation of ice. A third problem is the suboptimal operation of fuel cell when waste heat from the fuel cell stack is insufficient to bring the latter to the optimal operating temperature. A fourth problem is the need to have fuel cell system components that are specified to operate at freezing temperatures. While strategies are currently being used to mitigate the effect of freezing temperatures on PEM fuel cells, those conditions still lead to suboptimal operation and damage to membranes.
High ambient temperatures can also be a problem when the cooling subsystem is unable to keep fuel cells below a temperature limit where membranes and components can operate without damage. Either a disproportionately costly and energy consuming cooling system has to be used or the fuel cell has to be shutdown above an ambient temperature limit.
Finally, the deployment of stationary fuel cell systems is generally limited by their high cost. While fuel cell themselves have a high cost due to membranes and catalysts, stationary fuel cell system installations also bring the cost of hydrogen storage, the cost of installing the fuel cell systems and storage on a secure base, usually comprising concrete pads and fencing, with the required civil engineering costs.
Some have proposed solutions to the problems described above. One current practice (as disclosed by U.S. Pat. No. 6,479,177 B1) to avoid the formation of ice after shutdown in freezing conditions by purging the fuel cell tubing and stack of water. Another solution is to provide insulation and to heat the fuel cell when it is stopped in freezing conditions (see U.S. Pat. Nos. 6,955,861 B2, 6,797,421 B2, and 6,696,192 B1 as well as Published U.S. Patent Application No. 20030087139. U.S. Pat. No. 6,905,791 B2 describes the injection of an anti-freeze compound below a certain temperature. However, these solutions have drawbacks, such as consumption of energy for heating instead of providing power to external loads. The fuel cell system also has to work in varying temperature conditions, which requires a more adaptable, and therefore more costly, thermal management system. Purging water from the system does not solve the issue of slow start-up in freezing conditions. Also, these procedures do not address the issue of cooling when operating in extremely warm conditions.
Thus, those of ordinary skill in the art will recognize that there is a need for an improved solution to the above problems.